This invention is an improvement on the audio mixer system of Peters U.S. Pat. No. 4,149,032, which discloses a priority mixer control for a multiple microphone audio system that can accomodate two, three or even more microphones "on" simultaneously without noticeable dropouts and with effective automatic control of the overall system gain to preclude excessive feedback.
Although the systems disclosed in the U.S. Pat. No. 4,149,032 are of great utility, they are subject to several shortcomings. First, when the system is in a rest state, i.e., when there are no active talkers, the microphone channels could randomly gate on and off due to background noise in the room. There is no provision to assure that all microphone channels are off when the system is at rest. Alternatively, there are some situations in which it may be desirable to maintain one or more microphone channels in an "on" state even when there are no active talkers. Again, the patent does not disclose a means to allow such a set-up.
This invention impacts primarily on the idle or resting state of the mixer; i.e., when there are no active talkers. The improvements seek to overcome the above-mentioned shortcomings without compromising any of the unique features of the patent. The improvements provide for three different modes of operation in the rest state: first, a mode wherein all microphone channels are "off" in the rest state; second, a mode wherein just one microphone is "on" in the rest state; and third, a mode wherein just two microphones are "on" in the rest state. A mode select means is utilized to allow selection of one of the three modes.
With no active talkers (the system is in its rest state), the system microphones are subject only to background noise from sources such as air handling equipment, foot traffic, remote conversations, manufacturing noise and the like. Although such noise is normally low-level, random in time and space, and seldomly interferes with intelligibility, there are applications in which it is desirable to maintain all microphones in an "off" state when there are no active talkers. An example of such an application is a system in which the microphone channel status (on or off) is used as a source signal for controlling ancillary equipment such as television cameras or talker identification monitors. In such a system, momentary activation of a microphone channel, although perhaps audibly imperceptible, may lead to erroneous activation of the ancillary equipment.
There are other applications in which it may be desired or even necessary to keep one microphone channel "on" at all times. One such application is a radio or television broadcast, where the microphone mixer output is sent to remote listeners via a broadcast facility. During speaking pauses in such broadcasts, it is undesirable to have the microphone channels gate "on" and "off" due to ambient room noise, but it is also undesirable to have all channels "off", since remote listeners may depend on the microphones to transmit the room ambience. In such a situation, it is desirable to maintain one microphone channel "on" at all times in order to facilitate the transmission of the room ambience to the listening audience.
There are also applications in which it may be desireable to keep two microphone channels "on" at all times. In one such application two channels may be active with music signals. When there are talkers speaking simultaneously on any two channels, naturally occuring pauses in speech allow the system to update the "on" status of each channel without noticeable channel dropouts. Music, however, is a characteristically continuous signal, with no naturally occuring pauses to allow for updates. Any channel drop-outs which occur due to competition for system access are much more noticeable in music signals than in speech. Keeping two microphones "on" at all times eliminates the competition for system access and assures that the music signal will not be marred by channel drop-outs.